Forensic Biology is the analysis of body fluids such as blood and saliva for a criminal investigation. A stain is first identified and further testing is often performed to determine the possible origin. Genetic testing (DNA profiling) is the most prevalent type of analysis used to eliminate or include possible sources, most often the alleged crime victim, suspect or other involved party.
Forensic Biologist at some laboratory systems handle all evidence in their area from initial detection to identification and DNA testing and prosecution. Some use an “assembly line” approach, where one scientist may do only evidence screening, which means they only look for the body fluids, another would do tests to determine what the fluids are, and yet another would do DNA analysis. This approach allows the scientist to focus on a single area of expertise, although the “cradle to grave” approach gives a better overall understanding of the case and what may or may not be important based on related factors.
Depending on the agency, the forensic scientist may be trained in a variety of biological techniques or possibly just a single specialty, like DNA analysis. Some scientists also go to the crime scene and collect evidence. Most, however, have specialists known as Crime Scene Technicians that are dedicated to the task of initial evidence collection.
A Forensic Biologist begins their analysis by examining a piece of evidence for the presence of hairs, fibers and stains.
Any collected hairs or fibers of evidential value are most often transferred to a Forensic Microscopist for further analysis. However, it is usually the job of the Forensic Biologist to collect and preserve the hairs and fibers initially. Many times, an alternate light source, such as a laser is used to find stains on articles such as bed sheets or clothing. A portion of the stain is removed and tested for identification.
The most common types of tests are those for blood and semen, although at times it is necessary to test for other body fluids or tissues such as urine or saliva. A forensic scientist must know not only how to perform the appropriate test, but also how to interpret the results. Some tests can provide absolute answers, for instance, if a stain is in fact blood. Others can only provide a “likely” answer, like in the case of saliva, where there is no absolute conclusion. A positive analysis for this type of test means only that a substance is indicated (probable), not conclusively identified. Overstating conclusions is always a risk for the poorly trained or overly confident Forensic Biologist. Once a stain is identified, the scientist is often asked to determine who it could or could not have originated from. For example, if blood is found in a car, it may be beneficial to the case to find out if it originated from a homicide victim. In this scenario, DNA analysis would be conducted on the blood to develop a DNA profile. The resulting profile would then be compared to the DNA profile of the homicide victim. If the profiles are the same, they are considered a “match” and the next step is to figure out what that match means. How many other people could be expected to have the same profile? Depending on the amount of detail discovered in the DNA profile, this could range from a lot of people, to one in several billion, or essentially only a single person, i.e. the homicide victim. With this type of strong match, DNA analysis if very similar to a fingerprint, and the analyst is able to testify in court that the blood absolutely originated from a specific individual.